Known medicaments which have been used as antiulcer agents include H.sub.2 -receptor antagonists representative of which is cimetidine, gastric acid secretion inhibitors such as omeprazole inhibiting proton pump (H.sup.+,K.sup.+ -ATPase) and medicaments having gastric mucosa protection activity, which are chosen depending on the symptom of patients. However, those medicaments are of such disadvantages as generally weak activity and occurrence of side effects. For instance, cimetidine, representative of H.sub.2 -receptor antagonists have encountered the presence of intractable ulcer. Omeprazole has suffered from the occurrence of carcinoid and the interaction with other drugs including diazepam and phenytoin such as a lowering of hepatic clearance. Thus there is a continuing need for effective antiulcer agents.
The present invention results from efforts to develop new indole derivatives with more improved untiulcer effect.